The skin is an interface of an organism with the environment, prevents moisture loss from the body, and has a skin barrier function preventing the invasion of biotoxic substances, such as microorganisms and allergens, from the environment. Intercorneocyte lipids, ceramides in particular, and sebum in the stratum corneum are said to bear these functions. It is said that the stratum corneum must contain 10 to 20% moisture to function normally and maintain a healthy condition. The moisture is retained in the stratum corneum by the skin barrier function and flexibility and elasticity of the skin are thereby maintained.
When the moisture in the stratum corneum decreases, the stratum corneum loses the flexibility and is hardened. This causes chapping. In so-called roughened skin, i.e., a condition that the dermatoglyphic patterns disappear or are unclear, a significant decrease in the moisture content is observed in the stratum corneum. Roughened skin is not only a cosmetic problem of poor appearance but also a preliminary stage causing a skin disease, and has a pathological meaning. In addition, improvement of roughened skin makes a dried skin surface soft and smooth and further leads to an improvement of fine wrinkles.
It is known that when the skin barrier function of the stratum corneum decreases, the loss of moisture from the skin is serious compared with that in a healthy condition. In addition, an increase in transepidermal water loss (TEWL) through the skin is observed. This TEWL is closely involved in the barrier function and the moisturizing function of the stratum corneum and is used as an indicator of the skin barrier function.
Therefore, a healthy condition of the skin, i.e., a beautified skin condition, can be achieved by increasing the moisture content of the skin or suppressing an increase in TEWL.
Furthermore, recently, it has become a problem in animals, particularly in pets, that skin conditions are aggravated by influence of allergy or the like. The skin conditions can be improved and healthy skin conditions can be realized by moisturizing and protecting the skin.
Ceramides are one of human skin components and have skin-moisturizing and protecting functions and skin-roughness-preventing and improving effects. As cosmetics utilizing ceramides, skin cosmetic products containing a member of ceramide family, such as ceramides, glucosylceramides, and galactosylceramides, and diisopropylamine dichloroacetate or γ-aminobutyric acid are known (Patent Document 1). However, there are problems such that ceramides applied to the skin cannot reach nor be absorbed in the skin due to a barrier of epidermal lipids and that cosmetic ingredients other than ceramides cause irritation and inflammation.
In addition, health foods containing ceramides composed of sphingosine, a fatty acid, and a sugar, as an effective ingredient are also known (Patent Document 2). As the raw materials for the ceramides, composed of sphingosine, a fatty acid, and a sugar, those derived from Amorphophalus konjac and rice are commercially available. However, these raw materials contain ceramides in a low amount less than 3%. Therefore, in order to achieve the effects by oral ingestion, it is necessary to blend a large amount of the raw materials. In addition, since their prices are high, the health foods are unsatisfactory. Therefore, materials which can be readily ingested from daily food are desired.
Sphingomyelin accounts for about 30% of phospholipids in milk and has a structure in which phosphocholine is bonded to a ceramide skeleton composed of sphingosine and a fatty acid. Sphingomyelin is known to be present in the brain and nerve tissues in large amounts (Non-Patent Document 1). It is also known that sphingomyelin is slightly contained in food such as yolk.
It is reported that a sphingomyelin is absorbed through the small intestine in blood vessels when orally ingested (Non-Patent Document 2). In addition, it is known that a sphingomyelin in the stratum glanulosum of the skin is hydrolyzed by sphingomyelinase into a ceramide to be supplied to the stratum corneum (Non-Patent Document 3).
However, it has not been reported that the oral ingestion of a sphingomyelin can provide beauty effects, such as skin-moisturizing and protecting effects, skin-roughness-preventing and improving effects, and a wrinkle-preventing effect.
[Patent Document 1]: Japanese Patent Laid-Open No. Hei 01-22810
[Patent Document 2]: Japanese Patent Laid-Open No. Hei 11-113530
[Non-Patent Document 1]: Harper's Biochemistry, 24th Ed. 1997, 162.
[Non-Patent Document 2]: Schmelz, et al. J. Nutr. 1994, 124, 702-712.
[Non-Patent Document 3]: Uchida, et al. Seikagaku (The Journal of Japanese Biochemical Society) 2001, 73(4), 269-272.
It is an object of the present invention to provide a skin beautifier which has beauty effects, such as skin-moisturizing and protecting effects, skin-roughness-preventing and improving effects, and a wrinkle-preventing effect, by oral ingestion thereof and which contains a safe raw material derived from food as an effective ingredient. In addition, it is an object of the present invention to provide a skin-beautifying food or feed which has beauty effects, such as skin-moisturizing and protecting effects, skin-roughness-preventing and improving effects, and a wrinkle-preventing effect, by oral ingestion thereof and which includes a safe raw material derived from food.